Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1995-12-19
1997-07-29
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With light attenuation
356376, G01B 1124, G01B 1130
Patent
active
056526555
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a discriminator used upon being installed in a vehicle to discriminate the condition (snow-covered, gravel-covered, asphalt, wet, frozen, etc.) of the surface of a road on which the vehicle travels, and to an apparatus to which the discriminator is applied.
BACKGROUND ART
An antilock brake system (ABS) (or antiskid system) is a system for shortening vehicle braking distance as much as possible by controlling a brake so as to obtain a slip factor that maximizes braking force. Since a slip factor for maximizing braking force differs depending upon the condition of the road surface, it is necessary that the condition of the road surface be discriminated so as to carry out optimum ABS control suited to the conditions of the road surface. In addition, it is necessary to identify very bumpy gravel roads in order to absorb unpleasant vibration and maintain ideal riding comfort by controlling the suspension in conformity with the roughness of the road surface.
One technique for optically discriminating road surface conditions without contact is disclosed in "Road-Surface Condition Sensor Utilizing Polarizing Characteristic of Road Surface Reflection", by Toshio Takehana, Hikari Gijutsu Contact, Vol. 27, No. 3 (1989), pp. 158-164. According to this technique, a light-emitting element and a light-receiving element are arranged in such a manner that angle of incidence and angle of reflection take on the value of the Brewster angle (53.degree.). This utilizes the fact that since a wet road surface approximates a mirror surface, the degree of polarization approaches unity, whereas in the case of a dry road surface, the degree of polarization approaches zero.
However, this technique is such that an asphalt road surface is identified as being in either a wet condition or a dry condition; gravel roads and snow-covered roads cannot be discriminated. Further, since the angles at which the light-emitting element and light-receiving element are arranged are determined by the Brewster angle, precise positioning is required and the light-transmitting and light-receiving elements must be provided quite far apart.
Further, road-surface condition estimation suited for application to antiskid control is available ("Road-Surface Estimation Using Fuzzy Logic", by Katsuhiro Oba et. al., Jidosha Gijutsukai, Corporate Juridical Person, Gakujutsu Koenkai Zensatsushu 881, May, 1988, 881028). However, since this technique is suitable for application to an antiskid system, it lacks universality.
DISCLOSURE OF THE INVENTION
The present invention provides a road surface discriminator capable of being expanded to discriminate road surface conditions of a wide variety of types, thereby making many applications possible.
The basic structure of the road surface discriminator according to the present invention is as follows: Specifically, the road surface discriminator comprises a first light source for projecting light toward a road surface; a first spatial filter light-receiving optical system having first spatial filter means and first light-receiving means, wherein reflected light from the road surface on which light is projected from the first light source is received by the first light-receiving means through the first spatial filter means and the first-light receiving means outputs an electric signal representing the reflected light received; a second light-receiving optical system having second light-receiving means, Wherein reflected light from the road surface on which light is projected from the first light source is received by the second light-receiving means and the second-light receiving means outputs an electric signal representing the reflected light received; a first signal processing circuit for detecting intensity a center-frequency component, which corresponds to the spatial frequency of the first spatial filter means, from the electric signal outputted by the first spatial filter light-receiving optical system; a second signal processing circuit for detecting intensity of a low
REFERENCES:
patent: 4690553 (1987-09-01), Fakamizu et al.
patent: 4781465 (1988-11-01), Damachi et al.
patent: 5163319 (1992-11-01), Spies et al.
patent: 5218206 (1993-06-01), Schmitt et al.
Toshio Takehana, "Road-Surface Condition Sensor Utilizing Polarizing Characteristics of Road Surface Reflection", Hikari-Gijutsu Contact, vol. 27, No. 3, pp. 158-164 (1989).
Katsuhiro Oba et al., "Road-Surface Estimation Using Fuzzy Logic", Jidosha Gijutsukai Gakujutsu Koenkai Zensatsushu, pp. 109-112, (May, 1988).
Yasunobu Sakai et al., "Optical Spatial Filter Sensor For Ground Speed", Frontiers in Information Optics, Topical Meeting of the International Commission for Optics (Apr. 5, 1994), and Abstract.
Ishida Takeshi
Sakai Yasunobu
Takagi Junichi
Uno Tetsuya
Font Frank G.
Omron Corporation
Smith Zandra V.
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